The present invention relates generally to methods and systems for controlling a disc player after power has been interrupted and then reconnected. More specifically, the inventive method and apparatus provides a resume function for the disc player that restores the position of the disc pickup to its position prior to the power interruption.
Compact discs (referred to as xe2x80x9cCD""sxe2x80x9d)carry data recorded on a track that is in a spiral or concentric form on a recording medium. In a conventional CD player, a pickup device is conveyed radially across the CD. The pickup device is an optical pickup that relies upon radiating a laser beam onto the track and detecting changes in the reflected beam. Electronics within the CD player converts the sensed reflected signal to a digital bit stream. For an audio CD, this digital bit stream is subsequently converted to an audio signal.
One typical construction for a CD player is shown in FIG. 1. The disc player includes a motor 10 that rotates a platen supporting the compact disc D. A disc control microprocessor 12 controls the operation of the motor 10 to maintain a controlled speed of rotation for the disc D.
An optical pickup 14 is disposed beneath the recorded surface of the disc D. Signals generated by the optical pickup 14 can be provided to signal processing electronics within the disc player (not shown). In one type of CD player, the optical pickup 14 is carried by a fine actuator 16 that is operable to translate the pickup back and forth in a track access direction. This track access direction is substantially radial relative to the disc D. The fine actuator 16 is mounted to a carriage 18 that is propelled by a coarse actuator 20 through a transmission mechanism 22. The coarse actuator 20 can constitute a servomotor that operates the transmission mechanism 22 to translate the carriage 18 in the track access direction. In certain embodiments, the transmission mechanism 22 can constitute a rack and pinion device or a rotating drive screw.
Operation of the coarse actuator and transmission mechanism 22 provides coarse movement of the carriage 18, and consequently the optical pickup 14, relative to the disc D. On the other hand, the fine actuator 16 provides for smaller incremental motion of the optical pickup 14 relative to the disc D. In other words, the fine actuator 16 provides a finer tolerance movement of the pickup than is accomplished by the coarse actuator 20.
The fine actuator 16 can constitute an electromagnetic coil apparatus. Voltage applied to the coil apparatus causes the fine actuator 16 to translate the optical pickup 14 relative to the carriage 18. In the illustrated system, the fine actuator 16 maintains the optical pickup 14 in a neutral position in the absence of an impressed voltage to the actuator. A spring element 15 can be disposed between the pickup 14 and the carriage 18 to restore the pickup to the neutral position once the fine actuator 16 is de-energized. In contrast, the coarse actuator 20 does not maintain a neutral position for the carriage 18. Instead, the carriage 18 remains in its then current position when the coarse actuator 20 is de-energized. Typically, the coarse actuator 20 is servo-locked so that the carriage 18 will not change position even when the disc player is vibrated or jarred.
The operation of the fine actuator 16 is governed by a fine actuator controller 26. Signals are transmitted to and from the fine actuator 16 and actuator controller 26 by way of signal lines 25. Likewise, the coarse actuator 20 is governed by a coarse actuator controller 28. Signals pass on lines 27 between the controller 28 and the coarse actuator 20. The disc control microprocessor 12 transmits signals to and from the actuator controllers 26 and 28 along lines 29. For example, the disc control microprocessor 12 can provide a skip function for the disc player in which the optical pickup 14 is transferred between tracks of the recorded disc D. In this instance, the microprocessor may direct the coarse actuator controller 28 to undertake a gross movement of the carriage, and then command the fine actuator controller 26 to produce a smaller incremental movement until the pickup is positioned beneath the desired track. The optical pickup 14 can include a position sensor (not shown) that provides information to the disc control microprocessor 12 to ascertain the current track of information on the disc D.
The mechanics of the movement of the optical pickup 14 are depicted sequentially in FIG. 2. The figure presents a block diagram representation of the carriage 18 supporting the fine actuator 16, which is operable to translate the optical pickup 14. The carriage 18 is driven by the transmission mechanism 22 in response to the coarse actuator 20. As shown in the first position of FIG. 2(a), the optical pickup 14 is in its neutral position N. Preferably, this neutral position is generally centered relative to the carriage 18 and can be maintained by the spring 15.
When a voltage is applied to the fine actuator 16, the optical pickup 14 translates from the neutral position N to a position shown in the next figure of the sequence, FIG. 2(b). As the voltage impressed to the fine actuator 16 gradually increases, the actuator gradually moves the optical pickup 14 to its limit position LP, as depicted in FIG. 2(c). In the illustrated embodiment, the limit position is near one end of the carriage 18 and is disposed apart from the original neutral position N.
At the point in which the optical pickup 14 has reached its limit position, the pickup can be translated no further by the fine actuator 16. Thus, in order for the pickup to continue to radially traverse the surface of the recorded disc D, the carriage 18 must then be translated. The movement of the carriage 18 by operation of the coarse actuator is depicted in FIG. 2(d). As the carriage is translated, the optical pickup 14 remains in its absolute position LP relative to the disc D. Thus, the disc control microprocessor 12 must decrease the applied voltage to the fine actuator 16 so that the spring 15 draws the optical pickup 14 toward its centered neutral position N relative to the carriage 18. At the same time, and in a coordinated fashion, the carriage 18 is translated in an opposite direction radially outward relative to the disc D. With this coordinated movement, the optical pickup 14 is returned to its neutral position, now designated Nxe2x80x2, as shown in FIGS. 2(d) and 2(e). At that point, then, the fine actuator can be activated to further translate the optical pickup toward its new limit position.
As depicted in the sequence of steps in FIG. 2, the optical pickup 14 is consistently maintained to one side of the neutral position N. Alternatively, an opposite voltage can be applied to the fine actuator 16 to draw the pickup 14 to the left of the neutral position. In either case, the relocation of the carriage 18 relative to the optical pickup 14 requires cooperative control of the fine actuator controller 26 and the coarse actuator controller 27 so that the coarse movements of the carriage 18 do not disrupt the continuous reading of data from the disc D.
One problem faced by compact disc players arises when power to the various driving components is interrupted, or cut-off, and then subsequently restored. When power is interrupted In disc players having a spring-centered fine actuator, the lens may spring back over more than a minute of disc play time. On the other hand, CD players having only coarse actuators that can be servo-locked in position are generally difficult to tune to accurately and continuously read the recorded data in the small tracks of a compact disc.
A fine actuator, such as the actuator 16 depicted in FIG. 1, permits accurate positioning and tracking of the optical pickup 14 relative to the recorded medium. Circuitry can be provided within the disc player to provide feedback to the disc control microprocessor 12 and fine actuator controller 26 based on tracking error or focusing signals. However, the introduction of the fine actuator leads to a significant problem in restoring the position of the optical pickup to its last position when power was interrupted.
In some systems, the disc controller reads current sub-code information and table of contents (TOC) from the recorded disc. When power is interrupted, this information is stored in a local memory. When power is restored, the sub-code and TOC information is read and the optical pickup 14 is moved to the start of the recorded track before the normal operating mode, or play mode, is resumed. One disadvantage of this approach is that a certain portion of the data in the current track is necessarily re-read by the optical pickup, unless the power happens to stop at when the pickup is at the beginning of a track. In the case of an audio disc, the listener must hear same audio piece from the beginning if power is momentarily interrupted and then reconnected. In some cases, this error can be as large as the entire audio track, depending of course on the position of the optical pickup when power was interrupted.
In another approach, the current position of the optical pickup is maintained by continuously storing the current sub-code information in a non-volatile memory, such as an EEPROM or bubble memory device. When the power is reconnected, the system reads the sub-code information from the recorded medium, or disc, and compares that information with the stored sub-code information. The disc controller then calculates how far the optical pickup must jump to achieve the stored position of the pickup. After a proper amount of track jumping, the pickup is restored generally to its position prior to the power interruption, and the disc player resumes its play mode.
There remains a need for a disc player having a system that can accurately return the optical pickup to its position prior to a power interruption. There is further a need for such an apparatus and method that is readily adapted to a disc player having both fine and coarse movement control.
The shortcomings of prior resume control systems and methods are overcome by the present invention. To take advantage of certain features of the inventive apparatus and method, the disc player is provided with a coarse actuator and a fine actuator for controlling the radial movement of the disc pickup. The fine actuator is mounted on a carriage that is translated by operation of the coarse actuator. In one feature of the invention, the fine actuator is a coil-type actuator that translates the pickup in relation to a voltage applied to the actuator. In other words, as the magnitude of the voltage increases, the magnitude of the pickup travel increases. In accordance with this feature, the pickup returns to a neutral position when voltage to the fine actuator is interrupted.
In a preferred embodiment of the invention, the disc control electronics is augmented by an apparatus that stores information indicative of the magnitude of the voltage signal applied to the fine actuator. In a specific embodiment, the control signal from the disc control microprocessor is processed and stored in a non-volatile memory during the normal operation of the CD player. When power to the disc player is interrupted, this stored signal represents the position of the fine actuator relative to the carriage. De-energizing the fine actuator causes the pickup to return to its neutral position. When power is restored, the stored control signal is read by the disc controller and used to determine the control signal to be provided to the controller for the fine actuator. The fine actuator is re-energized with substantially the same voltage that was applied at the moment power was interrupted.
In another feature of the invention, the disc control microprocessor executes a sequence of steps in controlling the disc electronics during power interruption and resumption. In one embodiment, when power to the CD player is interrupted, the player is placed in a pause mode in which the disc continues to rotate but the disc player output is muted. The control microprocessor then determines an average position value of the disc pickup relative to the carriage over a predetermined number of disc revolutions. This average position value can be obtained by taking a numerical average of the fine actuator control signals provided by the microprocessor to the fine actuator controller. In a typical disc player, successive fine actuator control signals will vary as a function of tracking error or focussing signals supplied to the microprocessor.
This average value signal is stored in memory and the various disc controllers and motors are de-energized. When power is resumed, the drive controllers and motors are re-energized and the disc control microprocessor determines the current position of the disc pickup over a fixed number of disc revolutions. The same averaging method can be utilized to determine an average position of the pickup relative to the carriage. A comparison is made between this current position value and the position value stored in memory at the instant of the power interruption.
If the stored position value and current position value are equal, or in certain embodiments within a certain range, the disc control microprocessor unmutes the disc player output and normal play mode is resumed. On the other hand, if the two position values do not match, the control microprocessor directs the fine actuator controller to increment the position of the pickup relative to the carriage. In one embodiment, a fixed voltage increase is applied corresponding to movement of the pickup over a certain number of disc tracks or grooves. In one specific embodiment, the fine actuator controller can direct the fine actuator to jump the pickup over three grooves. The new position of the pickup is evaluated and compared to the stored position value. This process continues until the current and stored position values correlate.
It is one object of the present invention to provide a system and method for resuming normal operation of a compact disc player following a power interruption. A more specific object is to provide a resume function that restores the disc pickup to the position it had reached at the point of the power interruption.
One benefit of the apparatus and method of the invention is that minimal modifications are required to existing disc player electronics. A further benefit achieved by the present invention is that normal operation of the disc player can be faithfully resumed after a power interruption so that the disc player xe2x80x9cpicks up where it left offxe2x80x9d.
Other objects and benefits of the invention can be discerned from the following written description and accompanying figures.